[Digestion] Mixing in digesters?

[frank]

Dear Frank, and Biogas people,

Just a few questions if you don't mind.

Katahdin Energy Works wrote:

>Depends on the design.
>
>We do tanks, and depending on the % of solids may include a bubbler in the
>bottom of the tank. 
>  
>
What percent solids value do you to make this decision and what do you 
consider the optimum % solids?
And is the bubbler recirculating the gas that is produced in the tank?

>Other tanks include a heating core and agitator to have a uniform
>temperature.
>
>Temps are a concern; as is exposure to the two key microbe
>groups--Acetogenic and methanogenic. We use imbedded colonies to maximize
>exposure. 
>  
>
What is the optimum temperature you try to maintain and will the microbe 
activity be able to produce the needed heat without the need for outside 
heat source?

>There is a natural bubbling that occurs as solids sink to the bottom and get
>acting upon.
>
>CHD lagoons have a patented circulation system w/pumps and baffles.
>
>I haven't check evaluations of agitator systems; remember injection is from
>the bottom and that provides mixing; and digestion is from the bottom to the
>top.  
>
>In two tank designs; the acidification process is often a 'fast' one with a
>lot of agitation; while the methane one sees solids somewhat settling and
>methane given off bubbling to the top. 
>  
>
What is the optimum pH value for the system to work at optimum conditions?
Can the pH be used to control the CO2 given off?  Higher pH to keep the 
CO2 in solution , perhaps adjusting at the end?  to reduce the CO2 in 
the out gas.


>Hope this helps.
>  
>
It helps a lot as I am on a steep learning curve.
And the top of Mt Katahdin is my favorite place on Earth.

Thanks
Frank



>Frank J. Heller, MPA
>KATAHDIN ENERGY WORKS
>12 Belmont St.
>Brunswick, ME 04011-3004
>207.729.6090
>http://mysite.verizon.net/fjheller/
>
>
>-----Original Message-----
>From: digestion-bounces at listserv.repp.org
>[mailto:digestion-bounces at listserv.repp.org] On Behalf Of Harmon Seaver
>Sent: Wednesday, September 12, 2007 2:16 PM
>To: Digestion at listserv.repp.org
>Subject: [Digestion] Mixing in digesters?
>
>   Someone just posted that  "well-stirred digesters with mixed contents
>will always out-perform single feedstock digesters by volume". Sometime
>back, when I asked about having a mobile digester (to provide fuel for a
> motorhome and process waste), I was told that it would not work because
>disturbing the digester would cause it to stop working.
>    So is mixing bad or good?
>
>  
>

-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com